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- 实验方案
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Experimental Observation of Bound States of 2D Dirac Electrons at Surface Steps of the Topological Insulator Bi <sub/>2</sub> Se <sub/>3</sub>
摘要： Topologically protected surface states of three-dimensional topological insulators provide a model framework for studying massless Dirac electrons in two dimensions. Usually a step on the surface of a topological insulator is treated as a scatterer for the Dirac electrons, and the study of its effect is focused on the interference of the incident and scattered electrons. Then a major role plays the warping of the Dirac cone far from the Dirac point. The existence of another significant effect near the Dirac point brought about by the presence of steps is experimentally demonstrated here. Namely the band bending in the vicinity of steps leads to formation of 1D bound states in the corresponding potential wells. The observation of bound states in such potential wells in our scanning tunneling microscopy and spectroscopy investigation of the surface of the topological insulator Bi2Se3 is reported. Numerical simulations support our conclusion and provide a recipe for the identification of such states.
关键词： density of states,Dirac electrons,surface states,edge states,bound states,scanning tunneling microscopy,Bi2Se3,topological insulators,scanning tunneling spectroscopy
更新于2025-09-23 15:23:52
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Electron properties of topological insulators. The structure of edge states and photogalvanic effects
摘要： Integrating the ideas of topology and topological transitions into solid-state physics has led to the theoretical prediction and subsequent experimental discovery of topological insulators, a new class of three- or quasi-two-dimensional dielectric crystalline systems exhibiting stable conducting surface states. This paper briefly reviews the electronic properties of topological insulators. The structure of edge and bulk electronic states in two- and three-dimensional HgTe-based topological insulators is described in particular detail. Recent theoretical and experimental results on the interaction of an electromagnetic field with topological insulators and on edge and surface photogalvanic effects are presented.
关键词： photogalvanic effects,topological insulators,edge and surface states
更新于2025-09-23 15:23:52
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Photoinduced triboelectric polarity reversal and enhancement of a new metal/semiconductor triboelectric nanogenerator
摘要： We reported a novel metal/semiconductor triboelectric nanogenerator (TENG) based on Au and TiO2 as the friction layers. Upon illumination, the current polarity rapidly reverses compared to the dark state. The negative and positive short-circuit current approximately increase by 12 and 2 times, respectively. Particularly, a photocurrent plateau appears due to the formation of metal-semiconductor Schottky contact in the device. By carefully analyzing the charge transfer in dark and under illumination, it is found that the accumulation of a large number of photoelectrons on the surface of TiO2 and the increase of conductivity are the reasons for the reversal current polarity and significant current increase under illumination. Our work provides a new approach for improving TENG output and a new understanding about the effect of surface states on the triboelectric performance especially the polarity of TENG.
关键词： ultrathin Au,photoelectrons,triboelectric polarity reversal,Triboelectric nanogenerator,TiO2 surface states
更新于2025-09-23 15:23:52
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Depletion Layer Built-In Field at (1?100), (0001), and (000?1) GaN/Water Junction and Its Role in Semiconductor Nanowire Water Splitting
摘要： The nature of specific GaN plane/water interfaces under external bias and illumination can influence photoelectrolysis efficiency using GaN nanowires. Studies of Ga-polar, N-polar, and m-plane GaN interfaces with deionized water allow determining differences between surfaces corresponding to different nanowire facets. They are investigated under external bias conditions to reveal the profile of Fermi level localization through analysis of Franz–Keldysh oscillations using electrolyte electroreflectance (EER) technique in a specially designed measurement chamber. Calculation of the potential barrier height is also possible. EER study shows differences between surface densities of states (SDOS) at distinct GaN planes. One broad SDOS is identified near the conduction band in case of ±c-plane and related to Ga adatom reconstruction and β-Ga2O3 presence at the GaN electrode. Two narrow SDOS singularities are found at the m-plane one of which is localized near the middle of the bandgap and allows to generate approximately two times higher surface potential barrier than in case of polar surfaces at zero-bias conditions. This suggests that n-type GaN nanowires can enhance carrier separation at sidewalls and refine the oxygen evolution rate. Additionally, a voltage-controlled hysteresis loop of Fermi level localization is detected at the Ga-face GaN/water interface.
关键词： photoelectrolysis,m-plane,surface states,GaN,c-plane
更新于2025-09-23 15:23:52
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Realization of a three-dimensional photonic topological insulator
摘要： Confining photons in a finite volume is highly desirable in modern photonic devices, such as waveguides, lasers and cavities. Decades ago, this motivated the study and application of photonic crystals, which have a photonic bandgap that forbids light propagation in all directions1–3. Recently, inspired by the discoveries of topological insulators4,5, the confinement of photons with topological protection has been demonstrated in two-dimensional (2D) photonic structures known as photonic topological insulators6–8, with promising applications in topological lasers9,10 and robust optical delay lines11. However, a fully three-dimensional (3D) topological photonic bandgap has not been achieved. Here we experimentally demonstrate a 3D photonic topological insulator with an extremely wide (more than 25 per cent bandwidth) 3D topological bandgap. The composite material (metallic patterns on printed circuit boards) consists of split-ring resonators (classical electromagnetic artificial atoms) with strong magneto-electric coupling and behaves like a ‘weak’ topological insulator (that is, with an even number of surface Dirac cones), or a stack of 2D quantum spin Hall insulators. Using direct field measurements, we map out both the gapped bulk band structure and the Dirac-like dispersion of the photonic surface states, and demonstrate robust photonic propagation along a non-planar surface. Our work extends the family of 3D topological insulators from fermions to bosons and paves the way for applications in topological photonic cavities, circuits and lasers in 3D geometries.
关键词： 3D photonic topological insulator,split-ring resonators,Dirac surface states,robust photonic propagation,topological bandgap
更新于2025-09-23 15:23:52
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Surface passivation of GaAs (0?0?1) by Hg2Cl2 nanoplates combined with hexadecanethiol
摘要： Surface states in III–V semiconductor materials have detrimental effects on their optical and electronic properties, and the passivation of GaAs surface has become of longstanding interest. Here, we demonstrated a two-step process to greatly reduce surface states of GaAs (0 0 1) by a combination of Hg2Cl2 and alkanethiol. Firstly, uniformly distributed Hg2Cl2 nanoplates with a size around 200 nm were deposited on GaAs surface by the incubation of the etched wafer into the mercury (II) chloride solution, without the need of a reducing agent. Secondly, hexadecanethiol (HDT) molecules were assembled on the Hg2Cl2-GaAs hybrid surface, which decreases the density of surface states through electron transfer processes. Noticeably, after such two steps, a significant enhancement of photoluminescence (PL) signal was noted. It may be due to the fact that components of As2O3 and As0 which are identified as major sources of the surface states are reduced considerably, or even disappear. Chemical state changes of mercury species are expected to play a key role in achieving the surface passivation. Obtained hybrid GaAs materials with considerably improved photonic signals open a new avenue for the fabrication of electronic and optoelectronic devices.
关键词： Surface states,GaAs (0 0 1),Hg2Cl2 nanoplate,PL enhancement,Electrical passivation
更新于2025-09-23 15:22:29
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Acid-treated Ti4+ doped hematite photoanode for efficient solar water oxidation—Insight into surface states and charge separation
摘要： Acid-treatment has been proved to be an efficient approach to improve the photoelectrochemical (PEC) performance of hematite. However, efforts to optimize hematite photoanode have been limited by an inadequate understanding of the semiconductor surface. Here we make efforts to understand the microscopic charge separation processes of Ti4+ doped Fe2O3 photoanode before and after acid-treatment. Surface photovoltage (SPV) transient and the work function measurements directly reveal that acid-treatment leads to passivation of the surface states. Surface photovoltage (SPV) spectroscopic studies coupled to open-circuit photovoltage (OPV) measurements indicate that the surface states of hematite photoanode before acid-treatment result in the pinning of the Fermi level, which reduce the intensity of interfacial electric field at the semiconductor-electrolyte interface.
关键词： Water oxidation,Charge separation,Surface states,Hematite,Acid-treatment
更新于2025-09-23 15:22:29
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THz photodetector using sideband-modulated transport through surface states of a 3D topological insulator
摘要： The transport properties of the surface charge carriers of a three dimensional topological insulator under a terahertz (THz) field along with a resonant double barrier structure is theoretically analyzed within the framework of Floquet theory to explore the possibility of using such a device for photodetection purposes. We show that due to the contribution of elastic and inelastic scattering processes in the resulting transmission, side-bands are formed in the conductance spectrum. This side band formation is similar to the side-bands formation in cavity transmission spectra in an optical cavity and this information can be used to detect the frequency of unknown THz radiation. The dependence of the conductance on the bias voltage, the effect of THz radiation on resonances and the influence of zero energy points on the transmission spectrum are also discussed.
关键词： THz radiation,Floquet theory,surface states of topological insulators,side bands in transmission spectrum
更新于2025-09-23 15:21:01
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Surface modification of AlN using organic molecular layer for improved deep UV photodetector performance
摘要： Direct wide bandgap of 6.2 eV, high temperature robustness and radiation hardness make aluminum nitride (AlN) a preferable semiconductor for deep ultraviolet (UV) photodetection. However, the performance and reliability of AlN- based devices is adversely affected by a large density of surface states present in AlN. In this work, we have investigated the potential of a monolayer of organic molecules in passivating the surface states of AlN which improved the performance of AlN- based metal- semiconductor- metal (MSM) deep UV photodetectors. The organic molecules of Meso-5,10,15-triphenyl-20-(p-hydroxyphenyl)porphyrin Zn(II) complex (ZnTPP(OH)) were successfully adsorbed on AlN surface, forming a self- assembled monolayer (SAM). The molecular layer was characterized by contact angle measurement, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The surface modification of AlN effectively reduced dark current of the photodetector by ten times without degrading the magnitude of photo current, especially at low voltages. Photo to dark current ratio (PDCR) was enhanced from 930 to 7835 at -2V and the responsivity doubled from 0.3 mA/W to 0.6 mA/W at 5V. Moreover, the rise and fall times of the detector were found to decrease after the surface modification process. Our results suggest that SAM of porphyrin molecules effectively passivated the surface states in AlN which resulted in improved photodetector performance.
关键词： Dark current,PDCR,MSM UV photodetector,Surface states,SAM,Responsivity,Temporal response
更新于2025-09-23 15:19:57
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Subharmonic Shapiro steps in the a.c. Josephson effect for a three-dimensional Weyl semimetal WTe <sub/>2</sub>
摘要： We experimentally study electron transport between two superconducting indium leads, coupled to a single WTe2 crystal, which is a three-dimensional Weyl semimetal. We demonstrate Josephson current in 5 μm long In-WTe2-In junctions, as confirmed by the observation of integer (1, 2, 3) and fractional (1/3, 1/2, 2/3) Shapiro steps under microwave irradiation. The demonstration of the fractional a.c. Josephson effect indicates the multivalued character of the current-phase relationship, which we connect with the Weyl topological surface states contribution to the Josephson current. In contrast to topological insulators and Dirac semimetals, we do not observe 4π periodicity in the a.c. Josephson effect for WTe2 at different frequencies and power, which might reflect the chiral character of the Fermi arc surface states in a Weyl semimetal.
关键词： Shapiro steps,Josephson effect,Weyl semimetal,topological surface states
更新于2025-09-23 15:19:57